﻿using System;

namespace TrapezoidArea
{
    class TrapezoidArea
    {
        static void Main(string[] args)
        {
            Console.Write("Side A: ");
            double sideA = double.Parse(Console.ReadLine());
            Console.Write("Side B: ");
            double sideB = double.Parse(Console.ReadLine());
            Console.Write("Height: ");
            double height = double.Parse(Console.ReadLine());

            double result = ((sideA + sideB) / 2) * height;
            Console.WriteLine(result);
        }
    }
}
